1. Field of the Invention
The present invention relates generally to antennas and, more particularly, to end-fire array antennas.
2. Description of the Related Art
An array antenna is an antenna which has a plurality of radiative members that are arranged and excited to obtain a particular radiation pattern having a radiation maximum in a desired direction. The radiative members are generally spaced so that their radiation phases add in the desired direction.
Antenna arrays can be classified as linear or planar arrays and as broadside or end-fire arrays. In a linear or collinear array, the radiative members are arranged in a collinear relationship and in a planar array, the members are arranged in a planar relationship. If the array members are arranged so that their radiation phases add in a direction which is orthogonal to the line or plane of the array, the array is said to be a broadside array. End-fire arrays are typically collinear arrays and the array members are arranged so that their radiation phases add in a direction which is collinear with the array.
An exemplary end-fire array is a Yagi antenna (sometimes referred to as a Yagi-Uda antenna) which typically has a radiator spaced between a reflector and a plurality of directors. Because radiation energy is fed to the radiator it is sometimes referred to as the driven member and the directors are referred to as parasitic or passive members. The directors are spaced to obtain radiation phasing which enhances the antenna gain. The direction of the radiation maximum is generally collinear with the array members and opposite the reflector. The members of an end-fire array (and, therefore, a Yagi antenna) can have any conventional radiating structure (e.g., disc, patch or dipole).
End-fire array antennas (and, in particular, Yagi antennas) are described in various antenna references. For example, see Johnson, Richard C., et al., Antenna Engineering Handbook, McGraw-Hill, Inc., New York, third edition, chapter 3, pp. 12-17 and chapter 12, pp. 16-17. An exemplary end-fire antenna is disclosed in U.S. Pat. No. 5,440,319 which issued Aug. 8, 1995 to Raymond, Joel, J., et al., and was assigned to California Amplifier Company, the assignee of the present invention.
A large number of conventional Yagi antennas have been placed in service in antenna systems of various industries (e.g., the wireless cable industry). The reflector associated with these antennas is typically a simple back wall or a cup-shaped structure. Although antennas of this type can be economically manufactured and are generally effective, their value would be enhanced if their performance parameters (e.g., gain, side-lobe rejection and front-to-back ratio) could be improved. Preferably, such improvement would be obtained with a simple, low-cost structure which is configured so that existing in-service antennas could be similarly modified.